Zbigniew Michalewicz and David B. Fogel found this problem in a math text for fifth graders in the United States and gave it to many people, including undergraduate and graduate students and even full professors in mathematics, engineering, or computer science.

Take a strip of paper and fold it in half to the right. Then fold it in half again, in the same direction. Repeat several times, then open out so that each fold becomes a 90 degree turn. This example uses paracord instead of paper, but idea is the same.

Let’s say we want to estimate with Monte Carlo. We get some pairs of random numbers with both and uniformly distributed between 0 and 1. Approximately of those should fall within the unit circle, so we can get an estimate of by multiplying proportion of points that fall within that circle by 4.

Knowing that some implementations of pseudorandom number generators are better than others, we decide to take a look at the first 256 points. Can you tell which of the two pictures below shows uniformly distributed random numbers?